How to calculate the stratified means in a data frame?
Frank Duan <fhduan at gmail.com> writes:
Dear R people, I have a simple question to ask. Suppose I have a data.frame with two variables: one factor (x) and one numeric (y), I want to calculate the mean of y for each value of x. Although it's easy to do it within a for a loop, I believe there may be a concise way by using some kinds of "apply" functions. Could anyone tell me how to do that? Thank you.
tapply() will do that. (help(tapply), look at the "presidents" example).
O__ ---- Peter Dalgaard Blegdamsvej 3 c/ /'_ --- Dept. of Biostatistics 2200 Cph. N (*) \(*) -- University of Copenhagen Denmark Ph: (+45) 35327918 ~~~~~~~~~~ - (p.dalgaard at biostat.ku.dk) FAX: (+45) 35327907